The present invention relates to vehicle lifts, in particular of the scissors type. In the following description, scissors-type lifts mean in general scissors- and double-scissors-type lifts, in which, when the scissors are closed, the lift is lowered to ground level, and when the scissors are open, the lift is raised, and inverted-and double-inverted-scissors-type lifts, in which the scissors open beneath ground level, in order to lower the lift, and are closed at ground level in order to raise the lift, optionally with the assistance of pistons or rack-type mechanisms.
The FR-A-1 575 128 discloses a scissors-type vehicle lift comprising a volumetric operating system in which two cylinders move a vehicle lifting runway. A main cylinder receives the operating fluid directly from supply means, and a secondary cylinder receives the operating fluid from the outlet of the main cylinder, whereby with the runway there is associated the main cylinder and the secondary cylinder.
Scissors-type lifts have been developed in which, in order to move the lift, a pair of cylinders is provided for each of the lifting scissors of the runways. The known operating system for the cylinders is of the serial type, i.e. in a first runway there are disposed the main cylinders, the outlet of which supplies the secondary cylinders which are associated with the other runway. This arrangement requires temporally staggered raising of the two runways, and thus gives rise to a loss of parallelism of the vehicle relative to the ground. In addition, the force on the pair of cylinders is asymmetrical, with all the resulting problems.
The object of the present invention is thus to provide a volumetric operating system for vehicle lifts, in particular of the scissors type, which permits synchronized movement of the runways.
This problem is solved remarkably well by means of a volumetric operating system according to the present invention, for vehicle lifts. Further advantageous characteristics of the said system are indicated hereinafter.